Montana Yogo™ Sapphire

Yogo sapphires have been mined on and off since the late 19th century. Yogo sapphires range in colors from deep cornflower blue to lilac. Yogos have high clarity, few if any inclusions, no color zoning and when properly cut they are brilliant. Yogo sapphires are truly world class. Many of the corundum crystals tend to be flat. However, stones that cut to one carat or more are expected to increase as the depth of the proposed underground mining in initiated in the future. Yogos that cut out to two carats or larger are rare and extraordinarily beautiful.
Yogo sapphires are a variety of corundum found only in Yogo Gulch, part of the Little Belt Mountains in Judith Basin County, Montana, United States. Yogos are typically cornflower blue, which is a result of trace amounts of the elements of iron and titanium. They have high uniform clarity and are unique because they maintain their brilliance under artificial light. Because Yogo sapphires occur within a vertically dipping resistive igneous dike, mining efforts were historically focused on dike material readily available from surface mining. It is estimated that at least 28 million carats (5.6 tons or 5.5 long tons or 6.2 short tons) of Yogo sapphires contained in approximately 1,500,000 tons of previously unmined dike believed to exist between the old American mine and the British mine.
Fine jewelry containing Yogos was custom manufactured and given to First Ladies Florence Harding and Bess Truman. The vast majority of the previous production was accomplished by the British Syndicate between 1900 and 1928. Millions of carats were exported, cut and sold in Europe. It is believed that Yogos are in the crown jewels of England and the engagement ring of Princess Diana. Today, several Yogo sapphires and custom jewelry pieces made with Yogo sapphires are part of the Smithsonian Institutes gem collection, as well as other highly respected museums around the world.
Because Yogo sapphires occur within a vertically dipping dike that was injected into the Madison limestone formation, the dike lends itself to efficient and cost-effective modern-day mining techniques.
The term "Yogo" is a trademark and the designated brand name for sapphires found near Yogo Gulch, close to the town of Utica, Montana. Whereas "Montana sapphire" generally refers to gems found in other locations in Montana. More gem-quality sapphires are produced in the State of Montana than anywhere else in North America. Sapphires were first discovered in Montana in 1865, in alluvium along the Missouri River. Finds in other locations in the western half of the state occurred in 1889, 1892, and 1894. The Rock Creek location, near Phillipsburg, is the most productive site in Montana as of this date, but that will change when the Yogo mine is placed back into production.
In 1969, the sapphire was co-designated along with the agate as Montana's state gemstones. In the early 1980s, Intergem Limited, which controlled most of the Yogo sapphire mining at the time, rocked the gem world by marketing Yogos as the world's only guaranteed "untreated" sapphire, exposing a practice of the time wherein 95 percent of all the world's sapphires were heat-treated to enhance their natural color. Although Intergem went out of business due to gross mismanagement and questionable financial transactions, the sapphires it mined from the surface appeared on the market through the 1990s because the company had paid its salesmen in sapphires during its financial demise. Citibank had obtained a large inventory of Yogo Sapphires in the form of rough, cut and finished jewelry as collateral for a $5.0 million credit line. As a result of Intergem's collapse in 1985 and after Citibank keeping them in a vault for nearly a decade, Citibank sold its collection in 1994 to a Montana jeweler. Mining activity today is largely confined to hobby miners in the area. After being dormant for more than 34 year, the Yogo Mine was recently purchased by Yogold U.S.A. Corporation and is being evaluated to place back into commercial production.
The term "Yogo sapphire" refers only to sapphires from the Yogo Gulch. Unlike Asian, Australian and African sapphires, they maintain their brilliance in artificial light. Yogos present an advantage to gem cutters: since they are found as primary constituent minerals within an igneous matrix, rather than in sedimentary alluvial deposits where most other sapphires are mined. They retain a perfect or near perfect crystalline shape, making cutting much easier, as does their lack of inclusions, color zoning, or cloudiness. Yogos also exhibit a triangular pattern on the basal plane of the flattened crystals, with thin rhombohedral crystal faces, a feature absent in sapphires from other parts of Montana and around the world.
Yogos tend to be beautiful and very expensive. The United States Geological Survey and many gem experts have stated that Yogos are "among if not the world's finest sapphires." The roughs tend to be small, so cut Yogo gems heavier than 2 carats (0.40g) are unusual and highly desired. Only about 10-12 percent of cut stone are over 1 carat (0.20g). The largest recorded Yogo rough, found in 1910, weighed 19 carats (3.8g) and was cut into an 8-carat (1.6g) gem. The largest cut Yogo is 10.2 carats (2.04g). Because of the rarity of large rough Yogo sapphires, Yogo gem prices begin rising sharply when they are over 0.5 carats (0.10g), and skyrocket when they are over 1 carat (0.20g).
Montana sapphires in general come in a variety of colors, but Yogos are almost always blue. About two percent of Yogos are extremely rare purple or wine colored, due to trace amounts of chromium. A very small number of red rubies have been found at Yogo Gulch and these are even more rare and desirable than the purple colored Yogos.